One of the most common pumps for moving liquids or liquids containing suspended solids from place to place are centrifugal pumps. Typical applications include: irrigation, domestic water systems, sewage handling, pumping of drilling fluids or drilling muds, drainage of construction sites or underground structures and other such applications well known in the art.
Functionally, fluid is drawn through the pump by a spinning impeller positioned inside an annular volute. The volute has an eye at the center where water enters the pump and is directed into the center of the impeller. The rotation of the impeller flings the liquid outward to the perimeter of the impeller where it is collected in the volute for discharge out of the pump. As the liquid is driven outward because of the centrifugal force of the rotating impeller, a vacuum is created at the eye, which tends to draw more fluid into the pump.
A well-known limitation to the use of centrifugal pumps is their limited ability to draw fluid for self-priming when starting from an air-filled or dry condition. This difficulty is because the impeller is not capable of generating a sufficient vacuum when operating in air to draw liquid up to the pump when the standing level of the liquid is below the pump. Until liquid reaches the impeller, very little draw is generated by the impeller. Thus to begin pumping, the pump must either be primed manually or be self-priming.
Self-priming centrifugal pumps are well known, for example see U.S. Pat. No. 6,409,478, which describes a current state of the art self-priming centrifugal pump. Such pumps utilize a vacuum pump, such as a diaphragm pump, to supplement the minimal vacuum generated by the rotating impeller to draw sufficient water into the pump so that the pump may properly function.
With reference to FIG. 1, a self-priming centrifugal pump 2 is shown having a centrifugal section 4 operatively coupled to a vacuum priming section 6 and a vacuum pump 8. The centrifugal section 4 generally includes an intake 10 through which fluid is drawn by the impeller 12. The impeller 12 rotates on an impeller shaft 14 mounted in a bearing housing and operatively coupled to a means for driving the impeller shaft 14, such as an electric motor or combustion engine (not shown). As noted above, the rotation of the impeller 12 causes the fluid to be flung into the volute 16 and in turn the discharge outlet 18. A check valve 20 is used to substantially prevent the back-flow of discharged fluid into the volute 16. The process of self-priming in such a pump is well known in the art. Upon rotation of the impeller shaft 14, an operatively coupled vacuum pump 8 creates a vacuum, which is conducted to the vacuum priming section 6 by a vacuum hose 22. The vacuum draws fluid into the centrifugal section 4 and the vacuum priming section 6 thus priming the centrifugal pump 2.
Although centrifugal pumps are relatively simple and reliable, in the past, the valves and vacuum pumps used for self-priming have proven less reliable. As shown in FIG. 2 a current state of the art vacuum priming control system, such as that disclosed in U.S. Pat. No. 6,409,478, utilizes a vacuum-priming valve 24 which includes a valve body 25 connected to the vacuum pump (not shown) by the vacuum hose 22. The valve body 25 includes a valve stem guide, which guides the valve stem 28. The valve stem 28 works in conjunction with the valve seat to form a vacuum tight seal when the valve is closed, as is shown in FIG. 2. The lower end of the valve stem 28 is connected to a valve stem connecting rod 32, which in turn is connected to an upper compound lever arm 34. The upper compound lever arm 34 includes a pivot point 36, which is pivotally connected to bracket 38. A vertical connecting arm 40 is connected to the end of the upper compound lever arm 34 opposite that of valve stem connecting rod 32. The vertical connecting arm 40 is operatively coupled to the lower compound lever arm 42. The lower compound lever arm 42 is pivotally coupled to the bracket 38 at a lower pivot point 44. The lower compound lever arm 42 is also coupled to a float connecting rod 46 and float 48. In operation, when the fluid level in the vacuum priming section is low, the float 48 is drawn down by gravity and the gravitational force is transferred by way of the series of connecting arms to the valve stem 28. The transferred force opens the valve and thus allows a vacuum communication between the vacuum pump and the vacuum priming section. When the fluid level in the vacuum priming section is sufficiently high, the float is forced upward due to the buoyancy of the float 48. The force generated by the buoyancy of the float 48 is transferred by the series of connecting arms to the valve stem 28. The transferred force closes the valve, which prevents the fluid from being drawn up into the vacuum hose and thus the vacuum pump.
One of skill in the art should appreciate that the above prior art system may function well under certain ideal circumstances, however in many cases in actual operation the level of fluid in the vacuum priming section may be subject to variable and random level changes or turbulence which results in valve chatter. That is to say, the valve may be subjected to periodic opening and closing resulting in small amounts of fluid being drawn into the valve body. In certain circumstances, such as when fine suspended particles are contained within the fluid being pumped detritus and abrasive fine particles accumulate in the valve body and on the valve stem and valve guide. This accumulation of detritus and abrasive fine particles results in the binding of the valve stem within the valve guide and the overall deterioration of the functioning of the valve. In order to prevent this, substantial and time consuming maintenance must be performed on the vacuum priming valve to ensure proper functioning.
As a result of the above, there is a continuing and unmet need for a priming vacuum control system that is not subject to the chattering of the priming vacuum control valve when turbulence is experienced in the priming chamber. Further, there remains and exists a need for a priming vacuum control valve that is easy to maintain, and is not subject to the clogging, binding, and other functionally disruptive concerns exhibited by the current state of the art priming vacuum control valves described above.
The present invention is generally directed to a priming vacuum control system for use on a self-priming pump. Such a system includes a priming vacuum control valve and a priming vacuum control valve-actuating system. The priming vacuum control valve is disposed between a vacuum pump and a priming chamber for the self-priming pump so as to decouple the vacuum communication between the vacuum pump and the priming chamber when the priming vacuum control valve is closed.
In one illustrative embodiment of the present invention, the priming vacuum control valve includes: a valve stem positioned within a valve body, and a valve spring or other means for biasing, operatively positioned between the valve body and the valve stem so as to apply a default closing force between the valve body and the valve stem. One of skill in the art should understand and appreciate that the priming vacuum control valve of the present invention is a xe2x80x9cguidelessxe2x80x9d valve in that the valve stem is held in operative position by virtue of the default closing tension applied to the valve stem by the valve spring. That is to say, the relative axial position of the valve stem within the valve body is allowed to float and is not determined by the use of a valve stem guide as described by the prior art. Because the present invention eliminates the valve stem guide, the priming vacuum control valve of the present invention eliminates the inherent problems of sticking, poor performance and high maintenance exhibited by the prior art priming vacuum control valves.
The priming vacuum control valve is opened by the action of a priming vacuum control valve-actuating system. In one illustrative embodiment of the present invention, the priming vacuum control valve-actuating system includes a series of interconnected compound lever arms including an upper compound lever arm operatively connected to a float. The upper compound lever arm has a valve-actuating end which is disengagedly coupled to the lower end of the valve stem. The priming vacuum control valve-actuating system is designed such that a downward motion of the float within the priming chamber because of a lowering of fluid level within the priming chamber results in the transfer of a valve opening force to the upper compound lever arm. The valve-actuating end of the upper compound lever arm frictionally engages the lower portion of the valve stem and thus opens the priming vacuum control valve. One of skill in the art upon review and consideration of the present invention will appreciate that any valve chattering caused by the slight and/or irregular motion of the float within the priming chamber is significantly decreased.
The present invention also includes a self-priming pump, preferably a centrifugal pump that includes the priming vacuum control systems of the present invention. Also within the scope of the present invention is a priming vacuum control valve as is described herein for use with self-priming centrifugal pumps. The present invention also encompasses a method of retrofitting a self-priming centrifugal pump with the priming vacuum control systems of the present invention.
These and other features of the present invention are more fully set forth in the following description of preferred or illustrative embodiments of the invention.